Neurons is dissociated cell cultures, stained immunohistochemically with tetanus toxin, provide an optimal system for the quantitative study of the development of two-dimensional patterns of neurite outgrowth. Dendrite structural complexity, as measured by fractal dimension, increases exponentially over the first few days in culture and appears to be independent of the formation of intraneuronal contacts. Dendrite growth proceeds linearly for at least a week and does not parallel increases in fractal dimension. Fluorescently labeled reconstituted viral envelopes, applied to neuronal cell bodies, provide an effective vital stain for the axonal projections and synaptic terminals derived from the labeled neurons. Herpes virus has been used to mediate the transfection of the lacZ gene into neurons, providing a selective enzyme marker for synaptic terminals. Light and electron microscope immunocytochemistry have been used to localize the prion protein in neuronal cell cultures.